Data stored on optical recording media like DVD (digital video or versatile disk) or SACD (super audio compact disk) consists of a plurality of physical sectors. Each sector consists of 26 frames of a length of 91 data bytes each. Every frame is preceded by one of eight types of synchronisation codes SY0 . . . SY7 that do not occur in the 16/8 modulation used for encoding the data on the recording medium. These synchronization codes are located in the sector in the following pattern:
row# 0SY0frame# 0SY5frame# 1row# 1SY1frame# 2SY5frame# 3row# 2SY2frame# 4SY5frame# 5row# 3SY3frame# 6SY5frame# 7row# 4SY4frame# 8SY5frame# 9row# 5SY1frame# 10SY6frame# 11row# 6SY2frame# 12SY6frame# 13row# 7SY3frame# 14SY6frame# 15row# 8SY4frame# 16SY6frame# 17row# 9SY1frame# 18SY7frame# 19row# 10SY2frame# 20SY7frame# 21row# 11SY3frame# 22SY7frame# 23row# 12SY4frame# 24SY7frame# 25
The sequence of syncs through a sector is thus:                0 5 1 5 2 5 3 5 4 5 1 6 2 6 3 6 4 6 1 7 2 7 3 7 4 7        
Due to the special arrangement of the synchronization codes, decoders for decoding the data stored on the recording medium can easily synchronize their timing or re-synchronise after clock loss
During playback of optical recording media, different kinds of defects can occur, causing problems to the phase-locked loop (PLL) based acquisition system. If a defect occurs which can be detected by a disturbance detector (e.g. a black dot or a silver dot), the PLL is frozen and the correct number of frames is inserted. If, however, the defect cannot be detected by the disturbance detector (e.g. an interruption), the PLL can drift away and an incorrect number of frames is inserted. This problem is inherent to a PLL-based acquisition system and causes streaming loss until the start of the next sector. The same happens when a synchronisation code is inserted or a wrong synchronisation code is detected.